Method of shape recognition using postulated lines

ABSTRACT

A method for recognizing shapes is disclosed. A computer, such as a handheld computer with pen input, is used to receive a drawing from a user. The user&#39;s drawing is then analyzed to identify the location of potential vertices of angles or knots of splines using a technique of hypothesizing lines between known important points and calculating the distance between other points and that Postulated line. This process is repeated until all important points are located. Also disclosed is a method for determining whether a set of points is straight or curved.

REFERENCE TO COMPUTER PROGRAM LISTING APPENDIX

[0001] A computer program listing of the source code for the preferredembodiment of the invention is attached as an appendix hereto in thefile “code.asm” submitted on a compact disc with this application. Thisspecification hereby incorporates by reference that computer programlisting in its entirety. A total of two discs are submitted with thisapplication, one being a duplicate of the other.

BACKGROUND OF THE INVENTION

[0002] This invention relates to the field of computer software thatrecognizes shapes drawn by a user.

[0003] In the field of computer systems with graphical interfaces, it issometimes necessary for the computer to allow a user to draw a shape orfigure on the computer screen. Users typically draw shapes or figures onthe computer screen through an input device, such as a touch-sensitivescreen, mouse, track ball, tablet, or similar input device that capturesthe user's hand movements and translates these movements into figures onthe screen. In the field of handheld computers, many user interfacesemploy a stylus and a touch sensitive screen. For example, U.S. Pat. No.4,972,496 to Sklarew, “Handwritten keyboardless entry computer system,”discloses the combination of a touch-sensitive screen laid over a liquidcrystal display matrix. Computer systems that allows users to drawshapes directly on the screen by converting hand movements into“freehand” lines and curves on the screen are well known in the art.

[0004] A known problem with this freehand method of drawing is thatdrawings can appear to be unclear. Because these drawings are typicallydone without the aid of a straightedge or other drafting apparatus,lines and curves drawn by the user's hand can appear to be crooked,uneven, and jagged. Further, a touch sensitive matrix laid over adisplay screen sometimes has a lower resolution than the resolution ofthe display screens. This results in undesirable drawings that areunclear.

[0005] A solution to this problem is to program the computer system toanalyze the shapes drawn by a user, determine what shapes the user drew,and re-draw those shapes using straight lines and smooth curves. Suchsystems typically perform three steps.

[0006] First, this system allows the user to draw a freehand drawingthrough the use of an input device, such as a touch sensitive screen.Second, the system performs an analysis of the user's drawing. Third,the system erases the user's freehand drawing and draws a perfecteddrawing using the drawing analysis made in the prior step. This drawingis typically made through any of a number of prior art methods that arewell known in the field.

[0007] One prior art system described in Theo Pavlidis & Christopher J.Van Wyk, “An Automatic Beautifier for Drawings and Illustrations,”Siggraph vol. 19, pp. 225-234, San Francisco, Jul. 22-26, 1985[hereinafter “Pavlidis & Van Wyk”] used a clustering technique. Pavlidis& Van Wyk disclose a system that groups together sets of points drawn bythe user when the difference in values in the distance between adjacentelements is less than some small constant. Following this grouping, theclustering algorithm disregards clusters that are wider than some otherpredefined constant, and splits clusters in two when their widthindicates they may contain more than one line. The algorithm thenderives equations that can be used to draw lines. The Pavlidis & Van Wyksystem does not store or analyze data such as the order in which theuser drew each point or the speed with which each point was drawn. ThePavlidis & Van Wyk system produces undesirable results when it isapplied to drawings that contain a large number of points, especiallydrawings that contain closely overlapping lines, because it depends onthe proper prior selection of the aforementioned constants in order todistinguish between closely spaced lines.

[0008] Another prior art system disclosed by Bozinovic et al. in U.S.Pat. No. 5,544,265, “Shape recognizer for graphical computer systems”records the speed and trajectory of a stylus as it passes over a screen.Bozinovic discloses a system that analyzes drawings by determining linesegment end points and then determining whether segments between endpoints are straight or curved. Bozinovic does not disclose a method bywhich the system determines the location of the end points or how thesystem determines whether a segment is straight. Bozinovic requires anumber of computationally expensive calculations.

[0009] Another prior art system is described in Joaquim A. Jorge &Manuel J. Fonseca, “A Simple Approach to Recognise Geometric ShapesInteractively,” Departamento de Engenharia Informática, IST/UTL, Av.Rovisco Pais, 1049-001 Lisboa, Portugal [hereinafter “Jorge & Fonesca.”]Jorge & Fonesca analyzed drawings by calculating geometriccharacteristics of the user's drawing, and comparing these geometriccharacteristics to those of a set of known ideal figures. Jorge &Fonesca's method calculates the convex hull, smallest-area regularpolygons, perimeter and area scalar ratios of the user's drawing andcompares these characteristics with the characteristics of knownfigures. This method has the disadvantage of recognizing only thoseideal figures that were anticipated by the system's designers. If a userdraws a figure that the system's designers did not anticipate, it willnot correctly recognize it, because it will be unable to compare thedrawing's geometric characteristics with ideal geometric characteristicsfor that figure. This system also carries an undesirable risk ofincorrect analysis when two ideal figures, such as an isosceles triangleand a right triangle, have similar characteristics.

BRIEF SUMMARY OF THE INVENTION

[0010] A computer system that addresses some of the foregoingdeficiencies of the prior art is described. Software that recognizesshapes drawn by a user in accordance with the present invention analyzesa drawing by estimating the locations of important points in thedrawing. The computer system records both the points that comprise auser's freehand drawing and also the order in which each point was drawnrelative to the others. By iteratively locating the point in a drawingthat is farthest from a hypothetical line drawn through two of thedrawing's known or postulated important points, the system locates bothvertices of angles and closed plane figures as well as knot points forcalculation of a cubic spline.

[0011] Several objects and advantages of the present invention are:

[0012] To resolve the deficiencies of prior art mechanisms forrecognizing user-drawn shapes;

[0013] To recognize quickly arbitrary shapes drawn by a user;

[0014] To reduce the memory required to store a user's drawing bysimplifying a freehand scribble drawn by a user through therepresentation of that scribble as a set of points connected by linesand curves;

[0015] To recognize arbitrary shapes drawn by a user without the use ofcomputationally expensive functions;

[0016] To recognize line segments drawn by a user and distinguish themfrom other potential drawn shapes;

[0017] To recognize triangles, rectangles, and other closed figures withstraight sides drawn by a user and distinguish them from other potentialdrawn shapes;

[0018] To recognize figures comprised of a sequence of straight linesegments drawn by a user and distinguish those figures from otherpotential drawn shapes;

[0019] To recognize splines drawn by a user and distinguish them fromother potential drawn shapes;

[0020] To recognize ellipses drawn by a user and distinguish them fromother potential drawn shapes.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0021]FIG. 1 is a flow diagram illustrating the operation of a preferredembodiment of the present invention.

[0022]FIG. 2 is a flow diagram illustrating the “CALCULATE_SHAPE_SIZE”operation subroutine of FIG. 1.

[0023]FIG. 3 is a flow diagram illustrating the “FIND_IMPORTANT_POINTS”operation subroutine of FIG. 1.

[0024]FIG. 4 is a flow diagram illustrating the “ITERATE_FINDING_POINTS”operation subroutine of FIG. 3.

[0025]FIG. 5 is a flow diagram illustrating the operation of determiningwhether a set of points should be represented as a straight line segmentor a curve.

[0026]FIG. 6 is a flow diagram illustrating the operation of determiningwhether a scribble should be represented as a closed figure.

DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention is well suited for graphical computersystems or similar environments that allow the user to manipulateobjects through the use of an input device. The preferred embodiment isa pen-based computer, such as one with a touch-sensitive screen laidover a liquid crystal display matrix. The invention can also be embodiedin a computer system with a mouse, track ball, tablet, GlobalPositioning System-based device, or similar input device that capturesthe user's movements and translates these movements into figures on thescreen. The use of such devices to capture movements is well known tothose skilled in the art.

[0028] A pen-based computer system using the methods in accordance witha preferred embodiment of the present invention includes a centralprocessing unit, memory, input device, and operating system. One methodto practice and/or implement the invention is to program a standardprogrammable handheld computer, such as a computer capable of runningthe Palm OS operating system published by Palm, Incorporated of SantaClara, Calif. or a computer capable of running the Pocket PC operatingsystem published by Microsoft Corporation of Redmond, Wash. Theinvention can also be practiced and/or implemented with a standarddesktop, laptop, or notebook computer with an input device as describedabove and running a graphical operating system, such as the Windowsoperating system published by Microsoft Corporation or the MacOSoperating system published by Apple Computer of Cupertino, Calif. Theinvention's practice and implementation is not restricted to thesepotential embodiments.

[0029] The system takes as its input a string of points, representingthe user's drawing. As the user draws, the computer system determinesthe position of the input device several times per second. The precisetiming of this determination may vary depending on the specificimplementation, but for best results should occur as often as thecomputer's operating system can check the input device's position. Asthe user moves the input device, the computer system records thecoordinates of the input device and the order in which the pen passedthrough each coordinate. The preferred embodiment for this memorystructure is a stack or linked list of coordinate pairs, but can also beimplemented as an array. Thus, as the user draws, the system stores inits memory the points the user draws, and also the order in which eachpoint is drawn relative to each other point. Other information may bestored, such as velocity or timing of the user drawing movements, butthis other information need not been stored in the preferred embodimentof the invention. Any set of points associated with an order in whichthey were drawn, created, or otherwise generated shall be referred toherein as a “scribble.” One point on a scribble is said to be “between”two other points on the scribble if the point was drawn before one andafter the other.

[0030] When the user finishes drawing, the user typically so indicatesto the computer system through the use of an input device. In thepreferred embodiment, the user presses the pen into the touch-sensitivescreen while drawing and lifts the pen from the touch-sensitive screenwhen the drawing is complete.

[0031] After the user indicates the drawing is complete, the computersystem typically analyzes the scribble to guess what shape the userdrew. As used herein, “shape” means, for example: 1) a set of one ormore line segments connected to each other, such as a closed planefigure or angle, or 2) a planar curve, such as an ellipse or a cubicspline. The term “closed plane figure” is well known in the field ofgeometry. Closed plane figures are formed by three or more verticesjoined by line segments (or “sides”) such that each vertex is theendpoint of exactly two line segments. The terms “spline” and “knot” arewell known in the field of geometry. Splines are curves, which areusually required to be continuous and smooth. Splines are usuallydefined as piecewise polynomials of degree n with function values andfirst n−1 derivatives that agree at the points where they join. Theabscissa values of the join points are called knots.

[0032] Referring to FIG. 1, the recognition analysis begins at step 100,and proceeds to step 101 in which the analysis compares the number ofpoints in the scribble to the minimum number of points necessary for theanalysis to proceed. If there are too few points to analyze, therecognition aborts as unsuccessful. In an embodiment in which the userhas a drawing space of 160 pixels by 160 pixels, trial andexperimentation has revealed that it is advantageous to abort therecognition at this point if the user draws two points or fewer. Adifferent value can be computed for a different size computer screenthrough experimentation.

[0033] If there are an adequate number of points to analyze, flowproceeds to step 102. After initializing variables necessary for theindividual implementation of the analysis at step 102, flow proceeds tostep 103, in which the computer generates a single number representingthe size of the drawn shape. This number is preferably equal to thedistance in pixels between the two points in the scribble that arefarthest from each other.

[0034] Flow then proceeds to step 104, in which the scribble is analyzedto locate what are referred to herein as “important points.” As usedherein, an ““important points”means any of the following: endpoints ofline segments; endpoints of a spline; the first and last points of ascribble; vertices of angles; vertices of closed plane figures; andthose points in a curve that can be used as knots in the drawing of acubic spline. Important points are those points that are necessary forrecognizing the drawn shape and drawing the corrected, smooth version ofthe shape. The analysis in step 104 is described further in relation toFIG. 3 below.

[0035] Flow then proceeds to step 105, in which the computer systemdetermines whether it has found only two important points total and theshape size determined in step 103 is greater than a predeterminedconstant. In an embodiment in which the user has a drawing space of 160pixels by 160 pixels, trial and experimentation has revealed that it isadvantageous to use a number of approximately 50 as the predeterminedconstant in this step. A different value can be computed for a differentsize computer screen through experimentation. If the criteria of thiscomparison are met, the analysis ends at step 106, in which itpreferably returns the result of a line segment between the twoidentified important points. Otherwise, flow proceeds to step 107.

[0036] At step 107, the analysis determines how many straight sides arein the user's scribble. For each set of points in the scribble boundedby important points but containing no important points, the analysisdetermines whether the set should be represented as a straight linesegment or as a curve. This analysis is described further in relation toFIG. 5 below. Because this analysis involves analysis of aggregatestatistics derived from the distance between points that the user drewand a hypothetical line segment connecting two important points, in thepreferred embodiment this step is performed as part of the same loopthat performs step 104 above. It is shown here as a separate loop forthe purpose of clarity.

[0037] At step 108, the analysis determines whether the user has drawn aclosed figure. This analysis is described below in relation to FIG. 6.If the analysis concludes that the user has drawn a closed figure, flowproceeds to step 109; otherwise, it proceeds to step 116.

[0038] At step 116, the analysis determines whether the proportion ofstraight sides to curved sides is greater than a predetermined ratio. Inan embodiment in which the user has a drawing space of 160 pixels by 160pixels, trial and experimentation has revealed that it is advantageousto use a number of about 0.5 as the predetermined ratio in this step. Adifferent value can be computed for a different size computer screenthrough experimentation. Because this ratio can be highly determinativeto the recognition analysis, the preferred embodiment allows the user toconfigure the recognition system by adjusting this ratio. If theproportion of straight sides is equal to or greater than the ratio, flowproceeds to step 117; otherwise, flow proceeds to step 119.

[0039] At step 117, the analysis adjusts the locations of the importantpoints identified in step 104 in order to adjust angles to appear to beright angles. By reaching step 117, the analysis has determined that theuser has drawn a series of connected straight-line segments. Forexample, if the angles drawn by the user appear to be within about 10degrees of a right angle, the analysis moves the important points sothat the angles are about 90 degrees. Flow then proceeds to step 118,from which it preferably returns the result of a series of connectedstraight-line segments.

[0040] At step 119, the analysis has determined that there are fewerstraight segments than would be required to describe the drawing as aseries of connected straight line segments. The analysis thereforepreferably returns the conclusion that the user drew a spline.

[0041] If, at step 108, the analysis determines that the user drew aclosed figure, flow proceeds to step 109, in which the analysis conductsthe same comparison described above in relation to step 116. If theproportion of straight sides is approximately equal to or approximatelygreater than the ratio, flow proceeds to step 112; otherwise, flowproceeds to step 110.

[0042] At step 110, the analysis determines whether the scribble isshaped like an ellipse. This is preferably accomplished by firsthypothesizing two foci for the ellipse. One method of hypothesizing fociis to hypothesize the lengths of the semimajor and semiminor axes basedon the locations of those points in the scribble that are furthest fromeach other. When two foci have been Postulated, for each point in thescribble the analysis calculates the sum of the distances between thepoint and each of the two foci. The point is preferably counted as oneon an ellipse if the difference between this sum and what the sum wouldbe if the point were on an ellipse is within a predetermined range. Theanalysis deems the scribble to be shaped like an ellipse if apredetermined percentage of all points in the scribble are counted as onan ellipse.

[0043] If the analysis determines that the scribble is an ellipse atstep 110, the analysis preferably returns the result at step 113 thatthe scribble is an ellipse. Otherwise, the analysis preferably returnsthe result at step 111 that the scribble is a closed spline. A “closedspline” is a spline with more than two knots in which the first knot isat the same position as the last knot.

[0044] If, at step 109, the analysis determines that the proportion ofstraight sides is not approximately equal to or greater than thepredetermined ratio, flow proceeds to step 112. At step 112, theanalysis performs the same analysis described in reference to step 110above to determine whether the scribble is shaped like an ellipse. Ifthe analysis determines that it is not shaped like an ellipse, flowproceeds to step 115. If the analysis determines that it is shaped likean ellipse, flow proceeds to step 114. At step 114, the analysisdetermines whether there are more than, for example, 5 important pointsin the scribble. If there are, flow proceeds to step 113, returning theresult of an oval. If not, flow proceeds to step 115.

[0045] At step 115, the analysis performs the same adjustment ofimportant points described above in reference to step 117. Then, flowproceeds to step 120, at which the analysis preferably returns theresult that the user has drawn a closed plane figure.

[0046] Referring to FIG. 2, the analysis performs the calculation ofshape size as required by step 104 of FIG. 1 as follows. The subroutineis called at step 200, and proceeds to step 201. At step 201, theanalysis calls the FIND_FARTHEST subroutine with the first point in thescribble as an argument. The FIND_FARTHEST subroutine will be describedfurther below in relation to step 206. The FIND_FARTHEST subroutinepreferably returns that point in the scribble that is furthest from thepoint passed as an argument to it. At step 202, this result ispreferably stored in the variable p_far. The FIND_FARTHEST subroutine ispreferably then called for a second time at step 203, with p_far as anargument. At step 204, the result of the FIND_FARTHEST subroutine ispreferably stored in p_far2. At step 205, the distance between p_far andp_far2 is preferably calculated and returned as the shape size. Thestandard Cartesian distance function is preferably used. If p_far is apoint with Cartesian coordinates (x1, y1) and p_far2 is a point withCartesian coordinates (x2, y2), then the distance d between p_far andp_far2 is preferably calculated:

d={square root}{square root over ((x2−x1)²+(y2−y1)²)}  (1)

[0047] The FIND_FARTHEST subroutine's entry point is at step 206, atwhich the point passed to it is assigned to the variable p. Thesubroutine proceeds to step 207, at which the max_d variable isinitialized to zero and the max_point variable is preferably assigned tovariable q. At step 208, the subroutine begins to iterate through thepoints in the scribble. If no points remain in the scribble, flowcontinues to step 209. Otherwise, flow proceeds to step 210. At step210, the next point in the scribble is preferably assigned to thevariable q. At step 211, the subroutine calculates the distance betweenp and q, and assigns the distance to the variable d. At step 212, thesubroutine branches based on whether d is greater than or equal tomax_d. If yes, flow proceeds to step 213; if no, flow loops back to step208. At step 213, max_d is preferably set equal to d, and max_point ispreferably set to q, and flow then loops back to step 208. Step 208continues the loop, until all points have been considered. When allpoints are considered, flow proceeds to step 209, at which thesubroutine preferably returns max_point as the point furthest from pointp.

[0048] Referring to FIG. 3, the FIND_IMPORTANT_POINTS subroutine calledat step 104 in FIG. 1 begins at step 300. Trial and experimentation haverevealed that the most practicable way to implement both theFIND_IMPORTANT_POINTS routine and the ITERATE_FINDING_POINTS routinedescribed below in reference to FIG. 4 is to store all of the points inthe scribble in a random-access array, allowing the analysis to considerany point in any order. The array is preferably organized by having theposition of a point in the array directly correspond to the order inwhich it was drawn by the user. This array will be referred tohereinafter as the “scribble array.” The flow proceeds to step 301, inwhich the first and last points in the scribble array are automaticallydetermined to be important points. Flow proceeds to step 302, at whichvariables a and b are initialized, with a set to the index for the firstpoint in the scribble, and b set to the index for the last point in thescribble. Flow proceeds to step 303, where the subroutine branches basedon whether the first and last points in the scribble are the same point.If so, flow proceeds to step 306, where b is preferably set to the indexof the second-to-last-point in the scribble, and from there flows tostep 304. If the first and last points in the scribble are not the same,flow proceeds from step 303 to step 304. At step 304, the subroutinecalls the ITERATE_FINDING_POINTS subroutine with a and b as arguments.The ITERATE_FINDING_POINTS subroutine is described further in relationto FIG. 4 below. After this routine returns, at step 305 theFIND_IMPORTANT_POINTS subroutine terminates, having located theimportant points.

[0049] The ITERATE_FINDING_POINTS routine is described in FIG. 4. WhileFIG. 4 shows an implementation of ITERATE_FINDING_POINTS as a recursivesubroutine, other implementations are possible, including but notlimited to a non-recursive subroutine that stores arguments on aninternal stack. Referring to FIG. 4, ITERATE_FINDING_POINTS begins itsexecution at step 400, at which it is preferably called with arguments aand b, which represent indices to the scribble array. The subroutineflow proceeds to step 401, from which flow passes to step 402 if andonly if the difference between a and b is greater than a predeterminedbail_constant. In an embodiment in which the user has a drawing space of160 pixels by 160 pixels, trial and experimentation has revealed that itis advantageous to give the bail_constant a value of 4. A differentvalue can be computed for a different size computer screen throughexperimentation. Step 401 branches to step 412 if the difference is toosmall, but proceeds to step 402 otherwise. At step 402, the variable iis initialized to a+1, the variable max is initialized to zero, and thevariable max_i is initialized to zero. Flow then proceeds to step 404,which branches based on whether i is greater than or equal to b. If so,flow proceeds to step 403; otherwise, flow proceeds to step 406.

[0050] At step 406, the variable d is preferably assigned to thedistance between the point p[i], which is the point in the scribblearray referenced by the index i, and a Postulated line passing throughthe points p[a] and p[b]. The derivation and use of the formula forfinding the distance between a point and a line is well known in thefield of geometry, and is repeated here for the reader's convenience. If(x0, y0) is a point on a plane, and (x1, y1) and (x2, y2) are alsopoints on the same plane, then the distance d between (x0, y0) and aline passing through (x1, y1) and (x2, y2) is given by:$d = \frac{{{\left( {{y\quad 2} - {y\quad 1}} \right)\left( {{x\quad 0} - {x\quad 1}} \right)} - {\left( {{x\quad 2} - {x\quad 1}} \right)\left( {{y\quad 0} - {y\quad 1}} \right)}}}{\sqrt{\left( {{x\quad 2} - {x\quad 1}} \right)^{2} + \left( {{y\quad 2} - {y\quad 1}} \right)^{2}}}$

[0051] After step 406, flow proceeds to step 408, and from therebranches to step 409 if d is greater than max, and to step 411 ifotherwise. At step 409, max is preferably set to equal d, and max_i ispreferably set to equal i. Flow then proceeds to step 411. At step 411,i is incremented and flow loops back to step 404, until all points inthe scribble array have been analyzed.

[0052] Flow proceeds to step 403 from step 404 after the loop iscomplete. At step 403, flow branches to step 405 if max is greater thana predetermined tolerance value, and to step 412 if otherwise. Thetolerance value is preferably calculated beforehand, based on the sizeof the scribble. In an embodiment in which the user has a drawing spaceof 160 pixels by 160 pixels, trial and experimentation has revealed thatthe tolerance value should be calculated as follows: Set tolerance to be2 if the shape size is less than 25, to 5 is the shape size is less than50, and to 10 otherwise. A different set of values can be computed for adifferent size computer screen through experimentation.

[0053] At step 405, the point in the scribble array referred to by theindex max_i is preferably determined to be an important point. Flow thenproceeds to step 407. Step 407 recursively calls theITERATE_FINDING_POINTS function, with a and max_i as arguments. Afterthis recursive call returns, flow proceeds to step 410. Step 410recursively calls the ITERATE_FINDING_POINTS function, with max_i and bas arguments. Flow then proceeds to step 412. Step 412 terminates theroutine.

[0054] Referring to FIG. 5, the analysis determines whether a set ofpoints in a scribble between two important points resembles either acurve or a line segment as follows. Flow begins at step 500. From thereit proceeds to step 501, at which the variables w1, w2, w3, w4, and w5are initialized to zero. The analysis then begins to consider each ofthe points in the set of points in their scribble order. Flow proceedsto step 502, which branches based on whether there are any points leftin the set of points to consider. If so, flow proceeds to step 504,which takes the next point and assigns it to the variable p. Theanalysis then proceeds to step 505, which calculates as d the distancebetween p and a postulated line extending through the two importantpoints. This calculation uses the formula described in Equation 2 above.

[0055] After calculating d, flow proceeds to step 509. Step 509 branchesbased on whether d is greater than 5. If not, flow proceeds to step 511,which branches based on whether d is greater than 4. If not, flowproceeds to step 513, which branches based on whether d is greater than3. If not, flow proceeds to step 515, which branches based on whether dis greater than 2. If not, flow proceeds to step 517, which branchesbased on whether d is greater than 1. If step 509 determines that d isgreater than 5, flow proceeds to step 508, which increments the w5variable by one, and from there flow proceeds to step 511. Otherwise,flow proceeds from step 509 to step 511. If step 511 determines that dis greater than 4, flow proceeds to step 510, which increments the w4variable by one, and from there flow proceeds to step 513. Otherwise,flow proceeds from step 511 to step 513. If step 513 determines that dis greater than 3, flow proceeds to step 512, which increments the w3variable by one, and from there flow proceeds to step 515. Otherwise,flow proceeds from step 513 to step 515. If step 515 determines that dis greater than 2, flow proceeds to step 514, which increments the w2variable by one, and from there flow proceeds to step 517. Otherwise,flow proceeds from step 515 to step 517. If step 517 determines that dis greater than 1, flow proceeds to step 516, which increments the w1variable by one, and from there flow loops back to step 502. Otherwise,flow proceeds from step 517 to loop back to step 502.

[0056] If at step 502 the analysis determines that there are no morepoints in the set to be considered, flow proceeds to step 503. Step 503branches based on whether the ratios of w1 to the number of points, w2to the number of points, w3 to the number of points, and so on, fallswithin predetermined ranges. In an embodiment in which the user has adrawing space of 160 pixels by 160 pixels, trial and experimentation hasrevealed that it is advantageous to return the result that a side isstraight if the ratio of w1 to the number of points is greater than 0.21and the ratio of w2 to the number of points is greater than 0.42 and theratio of w3 to the number of points is greater than 0.53 and the ratioof w4 to the number of points is greater than 0.66 and the ratio of w5to the number of points is greater than 0.74. Comparisons to otherstatistical distributions are possible. A different set of values can becomputed for a different size computer screen through experimentation.

[0057] If the w-variables are within the predetermined ranges, flowproceeds to flow 505, which preferably returns the result that the setof points is straight. Otherwise, flow proceeds to step 507, whichpreferably returns the result that the set of points is curved.

[0058] Referring to FIG. 6, the subroutine called at step 108 in FIG. 1to determine whether the scribble is a closed figure begins at step 600.Flow proceeds to step 601, where the variable tol (an abbreviation of“tolerance”) is preferably initialized to an initial tolerance constant.In an embodiment in which the user has a drawing space of 160 pixels by160 pixels, trial and experimentation has revealed that it isadvantageous to use a number of approximately 6 as the predeterminedconstant in this step. A different value can be computed for a differentsize computer screen through experimentation. Flow proceeds to step 604,from which it branches based on whether the size of the scribble isgreater than a specified constant. In an embodiment in which the userhas a drawing space of 160 pixels by 160 pixels, trial andexperimentation has revealed that it is advantageous to define thisconstant as 50. A different value can be computed for a different sizecomputer screen through experimentation. The size considered in step 604is preferably the size calculated at step 103 in FIG. 1. If thecondition tested at step 604 returns true, flow proceeds to step 603,where the tol variable is preferably set to equal the integer of sizedivided by eleven. Flow then proceeds to step 602, which branches basedon whether tol is less than 2. If this condition returns true, flowproceeds to step 605, where tol is set to equal 2; otherwise, flowcontinues to step 606. If the condition tested at step 604 returnsfalse, flow proceeds to step 606. At step 606, the variable big ispreferably set to equal tol multiplied by 2, and the variable trigger ispreferably set to equal tol multiplied by 3. Flow then proceeds to step607, where the variable state is preferably initialized to zero, thevariable i is preferably initialized to zero, and the variable last_nearis preferably initialized to zero. Flow then proceeds to step 609. Step609 branches based on whether i is less than the number of points in thescribble and state is less than 2. If this is true, flow proceeds tostep 611. At step 611, the variable d is preferably set to equal thedistance between the first point in the scribble and the point in thescribble indexed by i. This distance may be calculated using the formulashown above as Equation 1. For speed of calculation, the preferredembodiment does not calculate the square root, and keeps d equal to thesquare of the distance between the two points. Flow proceeds from step611 to step 613, which branches based on whether state is greater than 0and d is greater than trigger. If this condition tests false, flowproceeds to step 615, which branches based on whether d is less thantol. If this condition tests false, flow proceeds to step 617, where thevariable near is preferably set to zero. Flow then proceeds to step 618,which branches based on whether near is equal to last_near. If thiscondition tests true, flow proceeds to step 620. At step 620, thevariable i is incremented, and the variable last_near is preferably setto equal near. From step 620, flow proceeds to loop back to step 609.

[0059] If the condition tested at step 613 is true, flow proceeds tostep 614. Step 614 sets the variable tol to equal big. Flow thenproceeds to step 615. If the condition tested at step 615 is true, flowproceeds to step 616. Step 616 sets the variable near to equal one. Flowthen proceeds to step 618. If the condition tested at step 618 is true,flow proceeds to step 619. Step 619 increments the state variable byone. Flow then proceeds to step 620.

[0060] If the condition tested at step 609 is false, flow proceeds tostep 610. Step 610 branches based on whether state is greater than one.If this condition is true, flow proceeds to step 612, which preferablyreturns the result that the figure is closed. If this condition isfalse, flow proceeds to step 608, which preferably returns the resultthat the figure is not closed.

[0061] In light of foregoing disclosures, the method for recognizingshapes in accordance with this invention provides a fast, flexible,preferably accurate method for representing a user's drawings as cleanshapes.

[0062] While the above description contains many specificities, theseshould not be construed as limitations on the scope of the invention,but rather as an exemplification of preferred embodiments thereof. Manyother variations are possible. For example, the constants describedabove can be made dynamic variables, which the user can adjust or whichcan be adjusted, for example, through an adaptive learning algorithm.Similarly, the invention can be applied to simplify the description of apath of movement taken by an object over terrain. Similarly, theinvention can be employed as a compression technique.

[0063] Accordingly, the scope of the invention should be determined notby the embodiments illustrated, but by the appended claims and theirlegal equivalents.

I claim:
 1. A method of recognizing shapes from a scribble, the methodcomprising the steps of: a. identifying one or more important points ina scribble; b. determining whether said scribble resembles a closedfigure; c. determining whether said scribble resembles a figure withmore straight sides than curved sides; d. recognizing said scribble as aline segment if said scribble has exactly two important points; e.recognizing said scribble as a straight curve if said scribble has morethan two important points and said scribble has more straight sides thancurved sides and said scribble is not a closed figure; f. recognizingsaid scribble as a spline if said scribble has more than two importantpoints and said scribble does not have more straight sides than curvedsides and said scribble is not a closed figure; g. recognizing saidscribble as a closed plane figure if said scribble has more than twoimportant points and said scribble has more straight sides than curvedsides and said scribble is a closed figure; h. recognizing said scribbleas a closed spline if said scribble has more than two important pointsand said scribble does not have more straight sides than curved sidesand said scribble is a closed figure.
 2. A method of identifying animportant point in a scribble between a first point in said scribble anda second point in said scribble, said first point not equal to saidsecond point and said first point not equal to said important point andsaid second point not equal to said important point, the methodcomprising the steps of: a. finding a third point on the scribblebetween said first point and said second point, such that the distancebetween said third point and a postulated line extending through saidfirst point and said second point is equal to or greater than thedistance between said postulated line and any other point between saidfirst point and said second point; b. identifying said third point as animportant point if the distance between said third point and saidpostulated line meets predetermined criteria.
 3. The method of claim 2,wherein said predetermined criteria includes comparing said distancebetween said third point and said postulated line to a constant value.4. A method of determining whether a set of points in a scribble, all ofsaid points in said set being between a first point in said scribble anda second point in said scribble, resembles either a curve or a linesegment, the method comprising the steps of: a. calculating the distanceof at least two points in said set of points from a postulated lineextending through said first point and said second point; b. concludingthat said set of points resembles a line segment if a statisticaldistribution of said distances meets predetermined criteria.
 5. Acomputer system that identifes an important point in a scribble betweena first point in said scribble and a second point in said scribble, saidfirst point not equal to said second point and said first point notequal to said important point and said second point not equal to saidimportant point, in which said computer system: a. finds a third pointon the scribble between said first point and said second point, suchthat the distance between said third point and a postulated lineextending through said first point and said second point is equal to orgreater than the distance between said postulated line and any otherpoint between said first point and said second point; b. identifies saidthird point as an important point if the distance between said thirdpoint and said postulated line meets predetermined criteria.